"The National Academy of Sciences is a private organization chartered by Congress to advise the government of scientific matters."
It is a shame that the National Academy of Sciences has allowed its reputation to be sullied by releasing a report with unsubstantiated assertions. This insistence that global warming is caused by humankind activity is nothing more than a new version of the "Chicken Little" story. Chicken Little concluded that the sky is falling because he got a bump on his head from something falling from the "sky." These academicians are saying that global warming is caused by humankind, instead of asking a few more questions about our natural climate change and variation. It is a shame to see questionable assumptions being recycled so boldly.
Your statement unfairly characterizes the noted scientific backgrounds of some of the panel members, who most certainly understand natural climate change and variation. Check out Karl Turekian as an example.